The general xerographic printing process used by printers, copiers and the like utilizes several well-known steps for making and transferring a latent image to a paper of other “substrate” material. A high voltage corotron wire emits charged particles via a coronal discharge process to uniformly charge the surface of a moving photoreceptor (“PR” or P/R”) having photoconductor qualities. The PR is often a circulating belt, but may also take the form of a rotating drum, for example. A metal grid and other electronic components typically regulate the PR charging levels.
When a section of the PR needing to receive a latent image advances to an exposure station, a copy of the image to be reproduced is sent to a laser. As will be described later, toner is used on the paper to represent the image pels or pixels. The laser is scanned over the PR in a raster-like manner exposing all locations of the PR where toner is desired (or alternatively, not exposing all locations on the PR where toner is desired using a negative convention). The light from the laser is thus modulated to correspond to the image to be copied, and the exposed areas of the PR discharge in the process. Consequently a latent image representing the image to be copied appears on the PR in the form of the pattern of charges on the PR surface.
In the developing step, toner particles are pre-charged and then loosely transferred to the discharged areas of the latent image on the PR to form a toner image. After the developing step, process control sensors such as toner area coverage (TAC) or extended toner area coverage (ETAC) sensors monitor the proportion of the area of the PR covered by toner to aid in image quality control. ETAC sensors, for example, can be used to optically measure the development control patch image characteristics. Other process control sensors that may be used include marks on belt (MOB) sensors that assure the exact placement of one color on top of another on an intermediate belt for proper color-to-color registration in a color image reproduction process.
In the transfer step, the paper to receive the image or an intermediate medium if applicable is pre-charged to a high level relative to the PR. The toner is then electrostatically transferred to the paper or medium from the PR to match the image to be copied.
In the cleaning step, residual toner particles are cleaned from the PR so that region is available to receive a new image without contaminating residue from an old image.
The last major step prior to outputting the paper is fusing the toner to the paper fibers under high temperature and pressure for a permanent finish.
Because of the airborne nature of small toner particles, many components of the reproduction device can become impermissibly coated or soiled over time. The components can include the various process control sensors, eventually causing them to operate out of the prescribed range and affect copy quality, requiring a service call to either clean or replace the sensors. In fact, many prior art electrostatic reproduction devices require such service calls after approximately fourteen thousand copies have been made.
One prior art approach exemplified by U.S. Pat. No. 5,809,375 issued to Alvin J. Owens et al. and also assigned to the assignee of the present application, is to filter the air inside of the device with a blower to circulate the air, and use one or more manifolds for filtering airborne toner and other particulate matter. While this may be successful in removing much of the airborne toner prior to the air exiting a customer replaceable unit (CRU), airborne toner and other particulate can still reach the process control sensors, whether directly or indirectly from the toner source from leaks in the filtering path and other causes. This may still lead to undesirable service intervals due to dirty sensor lenses. Further, adequate filtering using the blower and filter approach may not be adequate for keeping process control sensors clean at a cost necessary for low-end electrostatic image reproduction devices.
There is a great need to provide a mechanism for greatly extending the service intervals (for example, one million prints between service calls) for electrostatic reproduction devices related to process control sensor optical degradation. To that end, there is also a need to provide for the substantial reduction of toner and other particles and particulate matter around the lenses of process control sensors without introducing complex electromechanical components.